1. Field of the Invention
The present invention relates to a recording apparatus. More specifically, the invention relates to an ink-jet type recording apparatus for performing recording by ejecting ink toward a recording medium.
2. Description of Related Art
As a recording apparatus, an ink-jet type recording apparatus has been employed in various applications. Especially, a bubble-jet type printing apparatus which generates bubbles in ink and ejects ink droplets by pressure of the bubbles for recording by forming dots on a recording medium, is becoming majority. On the other hand, according to an increasing demand for color printing in the recent years, gradation of density becomes to be given importance in order to obtain an image close to the natural color. In order to certainly obtain satisfactory gradation, various systems, such as a system controlling dot density, a system varying size of the dot, a system for using different density of inks and so forth have been employed.
However, in the case of the system controlling the dot density, size of the ink droplet to be ejected has to be made smaller and thus to make the pitch of ink ejection orifices smaller. Smaller pitch of the ejection orifices may cause difficulty in production. As well, smaller pitch of the ejection orifices may increase possibility of causing clogging of the orifices. Furthermore, for higher recording speed, a greater number of ink ejection orifices are required so as to increase the overall size of the apparatus.
On the other hand, in the case of the system varying the size of the dot, while no problem will be arisen in the construction and the number of ink ejection orifices and liquid passages therefor, in the bubble-jet system to generate bubbles in the ink by heat, heat history management for varying response speed to change the size of the ink droplets becomes necessary for controlling generation of bubbles. Particularly, when an image has high recording density, non-uniformity of density tends to be caused at leading and trailing ends.
Furthermore, in the system using different density of inks, while no constraint condition is present on a head side, and achieving of gradation or gray scale is relatively easy, it inherently requires a large number of ink containers to degrade operability in installation and removal of the ink containers. Especially, in the case of serial type recording apparatus, in which a plurality of ink containers are carried on a carriage together with recording heads for performing recording, the carriage per se inherently becomes bulky.